1. Field of the Invention
The present invention relates to an acoustic processing technique for a short range radio communication headset, and more particularly to a headset communication system that realizes smoothing of communications by selectively adjusting and controlling necessary speeches from a plurality of types of speeches.
2. Description of the Related Art
A short range wireless communication system called Bluetooth has developed so that it becomes possible to connect and control devices such as PC, printer, portable telephone, digital camera, etc., within rooms or offices, without using any cords.
In this trend, in order to urge the application of the system to the mobile environment, there is a proposition to use a headset with a speech input function. The short range radio communication system centered around the headset with a speech input function is intended for communications and device controlling within about 10 m, which is a distance range visible by eyes. For this reason, in addition to the speeches transmitted/received through the radio communications, speeches directly uttered to a correspondent, speeches of a nearby third person, and noises will also reach to the user's ears. Consequently, there is a need for a technique to eliminate the unnecessary sounds according to the situation, such that only the necessary sounds can be extracted and outputted to the user's ears.
As the conventional speech processing techniques, the active noise control and the echo canceller technique for the long distance telephone lines are known. The active noise control tries to cancel all the arriving sounds without selecting the sound types. The echo canceller technique for the long distance telephone lines tries to cancel echoes. These techniques are not something that was developed for the short range radio communication headset so that it is difficult to apply them in their original forms.
FIG. 11 shows a feedback type active noise canceller used by a headset for acoustic use. A microphone 101 is mounted on a headphone mount, and the microphone signals are multiplied by some filter coefficient by the controller 105 and sent to a headphone speaker 103, and made to interfere with the external sounds to cancel them out. At this point, the filter coefficient is constantly adjusted such that the sounds picked up by the microphone becomes minimum. This is the feedback control for controlling output by feeding back the control target signals. The feedback type has a limit to the amount of noise reduction, but a configuration is relatively simple so that it is often used as the active noise canceller of a headset for acoustic use.
FIG. 12 shows an exemplary general method used for the noise removal. In the example of FIG. 12, the human voice alone is extracted from signals in which the human voice and the sounds coming from the headphone speaker 113 as a noise source are mixed.
Examples shown in FIG. 11 and FIG. 12 are not something that was developed for the short range radio communication system, and there has been no proposition conventionally of a method for comparing the sounds transmitted by the radio communications and the external sounds that are directly picked up, and reinforcing or reducing either one of them selectively according to the situation.